The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An automatic transmission generally includes a number of gear elements and torque establishing devices such as clutches and brakes. The clutches and brakes are selectively engageable to activate certain gear elements. Gear elements are activated to establish a desired speed or gear ratio between a transmission input shaft and a transmission output shaft.
The transmission input shaft is connected to an engine through a fluid coupling such as a torque converter. The transmission output shaft is connected to vehicle wheels. Shifting from one gear ratio to another may be performed in response to changes in throttle position and vehicle speed.
A shift from one gear element to another may be an upshift (i.e., a shift to a higher gear) or a downshift (i.e., a shift to a lower gear). The shift may be further defined as a power-on shift (i.e., a shift that occurs when an accelerator pedal is depressed) or a power-off shift (i.e., a shift that occurs when an accelerator pedal is released). Power-on shifts (upshifts and downshifts) may require more precise control than power-off shifts, as shifts that occur when a vehicle is accelerating may be more noticeable to a driver.